Research Article Novel Electrochemical Treatment of Spent...

Research ArticleNovel Electrochemical Treatment of Spent Caustic fromthe Hydrocarbon Industry Using TiBDD

Alejandro Medel1 Erika Meacutendez2 Joseacute L Hernaacutendez-Loacutepez1 Joseacute A Ramiacuterez1

Jesuacutes Caacuterdenas1 Roberto F Frausto1 Luis A Godiacutenez1 Erika Bustos1 and Yunny Meas1

1Centro de Investigacion y Desarrollo Tecnologico en Electroquımica SC Parque Tecnologico Queretaro-Sanfandila76703 Pedro Escobedo QRO Mexico2Facultad de Ciencias Quımicas Laboratorio de Investigacion Electroquımica Universidad Autonoma de PueblaCiudad Universitaria Edificio 105-i 72570 Puebla PUE Mexico

Correspondence should be addressed to Alejandro Medel alejandromedelreyesgmailcomand Yunny Meas yunnymeascideteqmx

Received 10 October 2014 Accepted 26 November 2014

Academic Editor Mika Sillanpaa

Copyright copy 2015 Alejandro Medel et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

During the crude oil refining process NaOH solutions are used to remove H2S H2Saq and sulfur compounds from different

hydrocarbon streams The residues obtained are called ldquospent causticsrdquo These residues can be mixed with those obtained in otherprocesses adding to its chemical composition naphthenic acids and phenolic compounds resulting in one of the most dangerousindustrial residues In this study the use of electrochemical technology (ET) using BDDwith Ti as substrate (TiBDD) is evaluatedin electrolysis of spent caustic mixtures obtained through individual samples from different refineries In this way the TiBDDrsquoscapability of carrying out the electrochemical destruction of spent caustics in an acidic medium is evaluated having as key process achemical pretreatment phaseThe potential production of ∙OHs as the main reactive oxygen species electrogenerated over TiBDDsurface was evaluated in HCl and H

2SO4through fluorescence spectroscopy demonstrating the reaction mediumrsquos influence on

its productionThe results show that the hydrocarbon industry spent caustics can be mineralized to CO2and water driving the use

of ET and of the TiBDD to solve a real problem whose potential and negative impact on the environment and on human healthis and has been the environmental agenciesrsquo main focus

1 Introduction

The aqueous residues produced by the hydrocarbon industrywhich involve the use of sodium hydroxide (NaOH) toremove hydrogen sulfide (H

2S) sulfhydric acid (H

2Saq) and

sulfur compounds found in different fractions of crude oilare known as spent caustics The process of producing saidresidues begins when an aqueous solution of NaOH is mixedwith a fraction of oil Although the oil itself can containsulfur the process is commonly carried out after the oilfraction is distilled due to its contact with air allowing theformation of H

2S which is very corrosive and difficult to

remove If the H2S is formed the NaOH reacts with it to form

sodium sulfide which is water soluble The spent caustics arealso obtained from different and specific processes whereby

they are classified as sulfidic spent caustics (removal of H2S

and mercaptans from hydrocarbons) naphthenics (removalof naphthenic acids from kerosene and diesel) and cresylicspent caustics (removal of organic acids phenols cresolsand xylenols) In the case of naphthenics and cresylicsthe NaOH reacts with the naphthenic acids leading to theformation of sodium naphthenates and phenolates respec-tively Accordingly and depending on the quantity and typeof products processed a refinery can generate spent caus-tics with multiple characteristics containing sulfide (S2minus 1ndash4wt) mercaptans (01ndash4wt) phenols (0ndash2000mg Lminus1)total organic carbon (TOC 6000ndash20000mg Lminus1) chemicaloxygen demand (COD 20000ndash60000mg Lminus1) biochemicaloxygen demand (BOD 5000ndash15000mg Lminus1) and potentiallytoxic elements (PTEs) such as Cu Ni Cd Pb and Cr among

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2015 Article ID 829136 18 pageshttpdxdoiorg1011552015829136

2 International Journal of Photoenergy

others [1] which require unconventional handling and treat-ment due to their highly toxic nature and unpleasant odor(the mercaptans can be detected in ppb) In the specific caseof spent caustics produced from olefins plants large amountsof S2minus (14000ndash21000mg Lminus1) pH values of 135 to 137 andemulsified hydrocarbons have also been reported [2] Withregard to the phenolic content depending on the refiningprocess it can reach up to 30600mg Lminus1 [3] The potentialdanger of the spent caustics can be understood consideringthe fact that by not having technology for its treatment insitu the different types of spent caustics can be combinedresulting in the production of highly toxic mixtures On theother hand when the spent caustics are not treated immedi-ately these are temporarily stored or confined by authorizedcompanies with their transport and storage being a latentthreat due to the possibility of spillage which has alreadybeen recorded in history with a highly negative impact onhuman health A concentration of phenol ranging from 5to 25mg Lminus1 is as toxic for aquatic life as it is for humans[4 5] For this reason the maximum limits allowed of phenolresidues found in industrial discharges vary between 05 and10mg Lminus1 [5] In the case of potable drinking water theEuropean Union (EU) in its 80778EC Directive assigned amaximum limit allowed oflt00005mg Lminus1 for phenol in all ofits forms [4] given that the consumption of water containingthese compounds can induce cancer or death [6] At the sametime the elevated danger of this contaminant for aquaticlife has marked phenol and some phenolic compounds aspriority contaminants in agreement with the criteria of theEnvironmental Protection Agency (EPA) of the United States[4 5] In a conventional manner the treatment of spentcaustics from refineries has been carried out in three steps(1) wet air oxidation (WAO) (2) acid neutralization (AN)and (3) biological oxidation (BO) On occasions step (2)can be followed by steam stripping After AN strippingremoves residual H

2S and mercaptans The liquid effluent

obtained has high BOD and COD concentrations becausethe major portion of the organic constituents is unaffected bythe stripping process Although WAO can treat spent causticto lower than 1000mg Lminus1 COD in 60min at 475K and 28bar the process is very expensive and due to severe reactionconditions safety is a major concern [2] At the same timethough the elimination of contaminants in steps (1) and (2)can lead to the obtainment of wastewater easily treatableby BO this depends strictly on the level of conversion andremoval of the contaminants found For example if the sulfurcontent is high and the concentration of phenols is low theBO (use of bacteria from the genus Thiobacillus) is possibleContrarily the process can be deactivated when the concen-tration of phenol is high It has been reported that effluentscontaining phenol with a concentration of gt3000mg Lminus1cannot be treated through BO [4] Taking this problem intoaccount different processes have been applied and evaluatedfor the treatment of effluents from refineries leaving asidethe treatment of the spent caustics It is important to mentionthat the physicochemical nature and composition of the spentcaustics is not comparable to wastewater produced as partof the extraction processes of crude oil (water produced)

or the wastewater produced in other processes In spentcaustics the content of phenolic compounds can reach avalue of 30600mg Lminus1 [3] while in water produced or anyother kind of wastewater this value can oscillate between20 and 200mg Lminus1 [7ndash9] In the case of wastewaters fromrefineries the chemical coagulation using polyaluminiumchloride [10] chemical precipitation [11] integrated processes(coagulation-flocculation and flotation) [12] and electroco-agulation (EC) has been reported to remove the high contentof the organic material found [13] At the same time andconsidering the importance of the phenolic content as wellas the content of commonly found fats and oils [14] theEC has also been evaluated using NaCl reaching removalpercentages of 91 [15] and 945 [16] for synthetic and realsamples respectively In other studies the combination ofelectroflotation (EF) and EC and integrated processes (EC-adsorption-BO) have also been proposed [17 18] Althoughin spent caustics the EC has been tested for the removal ofsulfides and organic material [1] it is important to highlightthat the nature of this process is not destructive allowing thetransference of the pollutants from one phase to another withthe subsequent disposal problemOn the other hand and con-sidering the technical difficulties in treating aqueous wastescontaining phenol or phenolic compounds through WAOBO or EC alternative processes of a destructive nature suchas the chemical advanced oxidation processes (AOPs in thepresence or absence of sunlight or assisted light) like theuse of hydrogen peroxide (H

2O2) ozone (O

3) photocatalysis

Fenton process and the ozonation in alkaline medium havebeen amply tested in the treatment of phenols and phenoliccompounds However the majority of these studies haveonly been carried out on synthetic samples In real samplesfrom refineries applying these processes only a few studieshave been reported [19]Considering the importance impliedin the treatment of real samples in the last years (2000ndash2014) different isolated studies have been reported on thetreatment of spent caustics using the Fenton process In thissense samples containing a COD of 20160mg Lminus1 and atotal of phenols of 1800mg Lminus1 have been successfully treatedobtaining removal efficiencies of 90 for COD and 99 fortotal phenols at a pH of 4 [20] At the same time whencomparing this process using assisted light (photo-Fenton)in the treatment of sulfidic spent caustics a greater efficiencywas reached with a removal of COD and sulfide up to 97and 100 respectively [21] Applying both processes anddespite the excellent results in practice the percentage oftotal destruction of the organic content is strictly dependenton the physicochemical composition of the sample to betreated An elevated organic charge consumes a large amountof H2O2 Also because of a high concentration of H

2S (up

to 20 g Lminus1) its reaction with ferric ion causes a loss ofiron catalyst activity [2] At the same time it is necessaryto emphasize that the chemical AOPs do not possess theability to destroy the reaction byproducts Contrarily oneof the most efficient processes and with the potential tocarry out the destruction of any contaminant including phe-nol and phenolic compounds is electrochemical oxidation(EO) Said technology bases its efficiency on the nature of

International Journal of Photoenergy 3

the material used as anode [22] In this sense two typesof anodic materials are known (i) active anodes (Au Nistainless steel (SS) Pt IrO

2 TiRuO

2 and analogous com-

binations) and (ii) inactive anodes (TiPbO2 TiSnO

2-Sb

and analogous combinations) which are materials with a lowor high production of ∙OH radicals (∙OHs) respectively The∙OHs can destroy any toxic pollutant to CO

2andwater due to

its high oxidation potential (28 V vs ENH) For this reasonthe use of inactive anodes is preferred Here it is importantto mention that Au Ni SS Pt and analogous combinationsare included due to their similar active or inactive behaviorThese materials are not included in the original referenceAlthough in the literature there are numerous studies relatedto the EO of phenol in synthetic samples [22ndash53] only afew studies have been reported applying this technology inthe treatment of samples from refineries and as far as weknow there are no reported studies on the treatment of spentcaustics It is also important to consider that both types ofaqueous residues represent a highly complex matrix whosechemical composition can favor or diminish the processefficiency According to this using a titanium (Ti) electrodecoated with titanium oxide and ruthenium oxide (RuO

2)

efficiencies of phenol degradation in 997 and 945 andoxidation percentages of COD in 889 and 701 wereobtained for synthetic and real samples (petroleum refin-ery wastewater) respectively [54] In other studies usingTiTiO

2-RuO2-IrO2for phenol degradation in wastewater

samples from refineries removal percentages of 7475 and48 for COD and TOC respectively were obtained evenwhen using high quantities of chloride ions [7] At thesame time the use of TiRuO

2-TiO2-SnO2has also been

evaluated in the hydrocarbon industry effluents obtaininglow percentages of phenol degradation around 20ndash47 [55]Ruling out the use of active electrodes and mixtures ofthese [56] a very important option is the use of TiSnO

2-

Sb and TiPbO2 which possess a high production of ∙OHs

however the application of these materials continues to berestricted due to structural problems and to the possiblerelease of Pb ions [57ndash59] As an alternative anodic materialthe boron doped diamond (BDD) has been amply evaluatedand accepted due to its unusual properties such as a highcorrosion resistance a low adsorption of organic compoundsgeneration of oxidizing species (O

3 H2O2 and ∙OH) [60]

and an elevated overpotential for the reaction of oxygenevolution 120578O

2[61] The BDD efficiency is based on its high

production of ∙OHs which are produced through the wateroxidation process (1) leading to the complete mineralizationof pollutants to CO

2and water (2) with high current

efficiencies [62] This process is known as electrochemicalincineration [22]

H2O 997888rarr ∙OH +H+ + eminus (1)

R +M (∙OH) 997888rarr M + 119898CO2+ 119899H2O +H+ + eminus (2)

It is important to emphasize that different studies on theoxidation of phenol and phenolic compounds in syntheticsamples using BDD have been presented from 2000 to 2014[63ndash86] demonstrating the capability of the use of BDDfor the destruction of these pollutants When comparing

the use of TiBDD with TiSnO2-Sb [87 88] and PbO

2[89]

it was found that the BDD electrode is much better for thedestruction of phenol Although the application of BDD inreal samples has been weakly explored when comparing theBDD with the electro-Fenton process for the treatment ofwastewaters from refineries it has been confirmed that eventhough the electro-Fenton process can induce a greater phe-nol degradation in comparison with the BDD electrode thegreater efficiency of degradation of the reaction byproducts(in terms of COD and TOC) occurs with BDD [9 90] Atthe same time other important studies applying the BDD forthe treatment of water produced and typical wastewater fromrefineries have demonstrated the great efficiency of BDD [91ndash93] Said studies and those previously presented not onlyhighlight the effectiveness of the use of the electrochemicaltechnology using BDD but also represent a platform whichimpulses the use of the BDD whose scaling potential mustbe examined in order to advance strategically in solvingreal problems According to the above and based on anextensive review of specialized literature from 1980 to 2014(use of national and international databases) the object ofthe present study is to demonstrate the technical feasibilityof the use of the TiBDD in the electrochemical treatmentof spent caustics mixtures one of the most toxic residues atan industrial level whose potential and negative impact onthe environment and human health is and has been the mainfocus of environmental agencies

2 Experimental Details

21 Chemicals Sulfuric acid (H2SO4) hydrochloric acid

(HCl) NaOH and phenol (C6H5OH) were obtained from

J T Baker K2HPO4 KH2PO4 NH4OH potassium ferri-

cyanide (K3Fe(CN)

6) and 4-aminoantipyrine (C

11H13N3O)

for analysis of phenol in all of its forms were obtainedfrom Aldrich Coumarin was obtained from Aldrich Theluminescent marine bacteria Vibrio fischeri (Photobacteriumphosphoreum) for toxicity analysis was provided by SDI

22 Instruments Analysis of phenol in all of its forms wascarried out through visible ultraviolet spectroscopy (UV-Vis) using a Lambda XLS+ spectrophotometer COD andTOCwere evaluated using aHachmodelDR200 reactorUv-Vis spectrophotometer DR2010 and Shimadzu Model TOC-VCSN equipment respectively COD was obtained usingHACH products Toxicity analysis was done using a DeltaToxkit provided by SDI Electrolysis using ultraviolet light(120582 = 254 nm) was done by using a Philips mercury lampwith 11W Orion Star A215 equipment was used for pHORPconductivity measurements The electrolysis experi-ments in galvanostaticmodewere performed using TektronixPWS4323 equipment The PTEs analyses were performedusing a Perkin Elmer Optima 3300 DVmodel and an Analyst200MHS-15 Perkin Elmer The first equipment was used forthe inductively coupled plasma (ICP) analysis and the secondfor the Hg analyses by hydride generation The morphologyand element analysis of the different electrodes evaluatedduring the selection of the best anodicmaterial were obtainedusing a scanning electron microscope (JEOL JMS-6060LV)


(a) (b)

(c)

Figure 1 Handling and control of (a) spent caustics mixture (b) safety equipment and (c) specialized infrastructure

equipped with an energy dispersive spectrometer (EDS)Crystal structure analysis using X-ray diffraction (XRD) wascarried out in a Rigaku Minifles using Cu K120572 radiation witha 30 kV operation voltage and 15mA of current at a velocityof 2∘min Cyclic voltammetry (CV) was carried out withan Autolab PGSTAT 30 The ∙OHs analysis was performedby fluorescence spectroscopy using the equipment HORIBAJobin MOD Fluorolog 3ndash22 with double monochromator

23 Characterization of the Spent Caustics

231 Sample Preparation A total of 10 samples (20 L each)of spent caustic were obtained from different refineries andstored at room temperature From these samples a compositesample was prepared by combining 1 L of each individualsample The sample obtained (called mixture) is shownin Figure 1(a) This process was carried out using safetyequipment (Figure 1(b)) andworking under an exhaust hoodwhich was attached to a gas scrubber containing NaOH(Figure 1(c))

Before taking each sample the container was stirredvigorously and the sample was taken immediately The mix-ture obtained was also stirred vigorously and stored underrefrigeration (4∘C) until its analysis

232 Physicochemical Analysis Before carrying out any anal-ysis the container of the mixture of spent caustics was stirredvigorously The PTEs analysis was done by using inductivelycoupled plasma atomic emission spectroscopy (ICP-AES)with the exception of Hg which was analyzed by hydridegeneration atomic absorption spectroscopy (HGAAS) Theanalysis was done prior to digestion of the samples Theconcentration of anions present was done through ion chro-matography according to the EPA method 3001 (EPA 1997)This analysis was performed using a high resolution liquidchromatograph Dionex ICS-2500 HPLCIC fitted with aDionex IonPac AS14A column and coupled to a conductivitydetector (ED50A) The mobile phase was Na

2CO3NaHCO

3

(1mLminminus1) The equipment was calibrated using preparedsolutions from the 7-Anion Standard of Dionex and thequality of the results was evaluated from the analysis ofthe certified standard of Inorganic Ventures IC-FAS-1AThe determination of volatile and semivolatile organic com-pounds (CIDETEQ and Intertek laboratories) in qualitativeform was done through gas chromatography mass spectrom-etry (GC-MS) in accordance with the EPA 5030EPA 8260C-2006 and EPA 3510EPA 8270D-2007 procedures Otherphysicochemical analyses were done under standard proce-dures It is important to highlight that during the entire


350 400 450 500 550 600 650 7000

1000000

2000000

3000000

4000000

5000000In

tens

ity (C

PS)

Wavelength (nm)(a1) (a2)

(a3) (a4)

(a)

(b1)

(b3)

(b2)

(b)

Figure 2 Experimental system for (a) hydroxyl radicalsrsquo analysis by fluorescence spectroscopy where (a1)ndash(a4) are the steps for analysis of

7-hydroxycoumarin and (b) electrolysis in galvanostatic mode of spent caustics mixture using TiBDD (b1) heat exchanger (b

2) rectifier

and (b3) electrochemical cell

process of preparation and analysis of the samples a strictsecurity protocol was followed from the use of a personalizedinfrastructure and safety equipment such as gas masksnitrile and neoprene gloves to that of a special suit

24 Electrochemical Treatment

241 Selection of the Anode Morphological structural andelectrochemical analysis of the different materials evaluated(TiIrO

2-Ta2O5 TiSnO

2-Sb and TiBDD) by SEM-EDS

XRD and CV were done over the same area (2185 cm2)TiIrO

2-Ta2O5and TiSnO

2-Sb electrodes were synthesized

by the thermal deposition method using a special formula-tion Polycrystalline boron ((B) = 1300 ppm)doped diamondfilm (TiBDD) of 3120583mthickness provided byAdamant Tech-nologies was synthesized by hot filament chemical vapordeposition (HF-CVD) The electroactivity of each materialwas evaluated by CV using a three-electrode cell (60mL

capacity with a reaction volume of 50mL) TiIrO2-Ta2O5

TiSnO2-Sb and TiBDD electrodes (2185 cm2) were used

as anodes a rod of Ti was used as cathode and a mercurysulfate electrode (HgHg

2SO4K2SO4(SAT) 119864∘ = 0640V

vs SHE) was the reference electrode The temperature wasmaintained at 298K and the voltammetric profiles for eachelectrode were obtained applying a scan rate of 100mV sminus1using 05MH

2SO4as the supporting electrolyte Before each

analysis the system was deoxygenated using N2gas In this

analysis the TiBDD was previously activated (to eliminateC-sp2 impurities) developing a special methodology [94]TiIrO

2-Ta2O5and TiSnO

2-Sb were activated by cycling

each electrode (50 cycles 100mV sminus1 in 05M H2SO4) to

stabilize the surface and eliminate impurities

242 Selection of the Reaction Medium Three aspects weretaken into account (i) the pH effect on the chemical state of


phenol (ii) the pH effect on the electrochemical response ofthe previously selected electrode and (iii) the pH effect onthe production of ∙OHs In the first point analysis by UV-Visspectroscopy to different pH values was performed with thegoal of identifying possible chemical changes on the phenolstructure In this analysis a synthetic sample was used Thesecond point was evaluated by the use of CV analyzing twotypes of acids HCl and H

2SO4(05M) under the same

conditions mentioned above The last point was evaluatedthrough electrolysis experiments which were performedapplying an anodic potential pulse (23 V vs HgHg

2SO4

polarization time of 10min use of a Pt mesh as counterelectrode 298K) This last analysis was performed throughthe use of fluorescence spectroscopy using coumarin (3 times10minus5M) as a probe compound to give way to the formationof the 7-hydroxycoumarin with a wavelength of maximumexcitation and emission of 332 nm and 500 nm respectively(120582ex = 332 nm 120582em = 500 nm) During electrolysis samplesof 10 120583L were withdrawn every minute and immediatelyanalyzed The equipment and the cell used for detection ofthe 7-hydroxycoumarin are shown in Figure 2(a)

243 Electrolysis of the Spent Caustic The electrochemicaldestruction process of the mixture of spent caustics wasdone in galvanostatic mode using the experimental systemshown in Figure 2(b) In this process a cell with a singlecompartment and a capacity of 120mL (reaction volume of100mL 8 rpm 298K and TiPt (3 cm2 as counter electrode))was used The area of the anode (prior selection) was 3 cm2Electrolysis with UV light (120582 = 254 nm) was done underthe same conditions indicated above In each experimentrepresentative samples were taken at different reaction times(119905119903) and the degradation of aromatic compounds (phenol and

phenolic compounds) and reaction intermediates was donethrough TOC and COD analysis

The removal percentages were calculated according to thefollowing formula (3) where 119862

119900is the initial concentration

(mg Lminus1) and 119862119891is the final concentration (mg Lminus1) [90]

removal = [(119862119900minus 119862119891)

119862119900

] lowast 100 (3)

The phenol analysis was done using a standard procedure[95] while the toxicity tests were done using a standardmethod using a lyophilized bacteria Vibrio Fischeri (Photo-bacterium phosphoreum) of a luminescent nature where thereduction of light is proportional to the degree of toxicity

3 Results


311 Physicochemical Analysis Table 1 shows the resultsobtained in the physicochemical characterization of the sam-ple corresponding to themixture of spent caustics (mixture of10 samples) Comparatively it shows the analysis of a simplesample corresponding to the sample of greater toxicity(preliminary evaluation of the phenolic content) including

the reported values in the literature for spent caustics as wellas for wastewater from refineries [1 3 7 9 13 16ndash19 96ndash98]

The analysis of the mixture showed a phenolic content of1104174mg Lminus1 while the simple sample showed a content of727089mg Lminus1 The difference between both samples clearlydemonstrates the environmental problem that commonlyappears in the hydrocarbon industry That is to say residuesof low or high toxicity are mixed with each other resultingin a residue of greater toxicity Here the phenol concentra-tion organic load and dissolved solids are not comparablewith any other residue including wastewater from differentrefining processes [90] The phenol concentration in thesamples analyzed suggest that this residue cannot be treatedby BO (a concentration gt3000mg Lminus1 leads to the completedeactivation of the microorganisms) This is confirmed bythe result obtained in the toxicity tests (100 toxic) andthrough the analysis of the BOD

5COD = 009 and 007

for the simple sample and the sample corresponding tothe mixture respectively On the other hand the elevatedalkalinity (5226635mg Lminus1) and an elevated pH (13ndash135)reflect the reducing nature of these residues which shouldbe considered in the treatment to be chosen Many of thecontaminants can be fixed at an alkaline pH and be liberatedunder oxidizing conditions The reactivity analysis for sul-phides and cyanides showed values below the detection limit(lt3729 and lt025mg Lminus1 resp) Based on the resultsobtained in this phase of characterization the samples evalu-ated were classified as cresylic spent caustics

312 Ion Analysis The analysis of anions done throughion chromatography in the case of the simple sampleshowed a low content of chlorides (Clminus) and sulfates (SO

4

minus2)with values of 86 and 608mg Lminus1 respectively with theirconcentration being much higher in the mixture with valuesof 54900 and 1882mg Lminus1 respectively It is necessary tomention that in this case the presence of chlorides is veryimportant The chlorides while they can give rise to thepresence of compounds of greater toxicity can also exerta synergic effect during an EO process giving way to theformation of different oxidizing species [99 100]

313 Analysis of Volatile and Semivolatile Organic Com-pounds An analysis through GC-MS corresponding to themixture of spent caustics was carried out to determine thedifferent phenolic compounds (reflected in the analysis ofphenol in all of its forms Table 1) Different compoundswere considered of which 43 were for volatile and 62 forsemivolatile analysis The results showed only the pres-ence of 24-dimethylphenol phenol m-methylphenol p-methylphenol and o-methylphenol all highly toxic com-pounds Figure 3 shows the representative chemical struc-tures of each compound identified

At the same time a PTEs analysis through ICP wascarried out taking into account that the physicochemicalcomposition of the mixture of spent caustics includes PTEsand possible catalyst traces used in the different processes ofhydrocarbon refining The selection of each PTE was basedon an extensive bibliography review Table 2 shows the main


Table 1 Physicochemical analysis of spent caustics

Parameter Value Value referenceSimplesample Mixture Spent caustic Typical refinery wastewater

Total phenol (mg Lminus1) 727089 1104174 30600 [3] 13 [16] 17250 [18] 317 [17] 19290 [9] 141 [7] 113[19] 23 [96]

Oil and grease (mg Lminus1) 23970 339970 mdash 85 [97] 196 [17] 1270 [19] 15 [98]BOD5 (mg Lminus1) 6930 7811 mdash 323 [97] 4025 [16] 570 [3]

COD (mgO2 Lminus1) 72065 98750ndash

10284250 72450 [1] 320100 [3] 3150 [97] 100 [16] 4450 [18] 2323 [13] 257 [17]590 [9] 602 [7] 935 [19] 2746 [98] 1220 [96]

BOD5COD 009 007 mdash 060 [19]Sulfides (mg Lminus1) lt3729 lt3729 34517 [1] 48500 [3] 19 [19]Ammonia (mg Lminus1) mdash mdash mdash 1310 [19]Cyanides (mg Lminus1) lt025 lt025 mdash mdash

pH 1302 1350 1297 [1] 13 [3] 8 [16] 860 [18] 805 [13] 760 [17] 920 [7] 810[19] 759 [98] 10 [96]

TOC (mg Lminus1) mdash 2013750 53900 [3] 370 [19] 1500 [96]Hydrocarbons (mg Lminus1) mdash mdash mdash 1172 [17] 002 [19]Conductivity (mS cmminus1) 12920 20844 12670 [1] 6 [18] 1306 [13] 1563 [7] 173 [7] 006 [98]Alkalinity CaCO3 (mg Lminus1) 5226635 mdash 15500 [3] 3990 [96]Total dissolved solid (mg Lminus1) mdash 169680 mdash 5000 [18] 7990 [13] 1333 [7] 4380 [98]Settleable solids(mg Lminus1) mdash 40 mdash mdash

Total suspended solids(mg Lminus1) mdash 3940 mdash 2280 [16] 35 [18] 100 [13] 1000 [96]

Toxicity () 100 100 mdash mdashFminus (mg Lminus1) 50 135 mdash mdashClminus (mg Lminus1) 86 54900 37900 [3] 63 [97] 112 [7] 200000 [96]Brminus (mg Lminus1) 12 lt030 mdash mdashNO3

minus (mg Lminus1) 11 lt025 mdash mdashPO4

3minus (mg Lminus1) 381 lt030 4600 [3] mdashSO4

2minus (mg Lminus1) 608 1882 20300 [3] 105450 [13] 212 [7] 1650 [96]ORP (mV) minus33420 mdash mdash mdashTurbidity (NTU) mdash mdash mdash 610 [16] 37 [17] 37 [19]

PTEs identified in the mixture sample In this analysis ahigh amount of Na+ and Fe with values of 19148mg Lminus1and 1323mg Lminus1 respectively was identified The presenceof Na+ confirms the caustic nature of the sample while thepresence of Fe though it is not an especially toxic elementis commonly controlled by the effect of turbidity caused bythe precipitation of oxides and hydroxides The analysis of Fewas done taking into account its catalytic activity onH

2O2 to

giveway for the ∙OHthrough the Fenton reaction [90]Due tothis the presence of Fe could be used to accelerate the min-eralization process and decrease the residence times duringthe EO process

On the other hand PTEs like As and Cd remainedunder the detection limit (lt0098 and lt0114mg Lminus1 resp)while Cu Cr Hg Ni and Pb exceeded the maximum limitsallowedunder theMexicanRegulation [101] It is important tohighlight the elevated toxicity of said elements and speciallythat of the Hg [102 103] and Pb which have the ability to

enter into the food chains and to concentrate in organisms(magnification process) Considering these analyses theelevated toxicity of the spent caustics is confirmed thusjustifying the need to direct efforts towards their treatmentandor destruction


321 Selection of the Anode Morphology elemental com-position crystal structure and electrochemical analysis Theresults corresponding to these analyses are shown in Figure 4Themorphology of metal oxide coatings (TiIrO

2-Ta2O5and

TiSnO2-Sb) (Figures 4(a) and 4(b) resp) showed smaller

cracks in comparison with TiBDD (Figure 4(c)) The lattershowed a compact structure demonstrating the quality of thecoating and the adherence of the diamond to the titaniumsubstrate In parallel X-ray dot-mapping was used to analyzethe distribution of coating elements


Table 2 Analysis of PTEs in spent caustics mixture

MLA (mg Lminus1) in riversPTE (mg Lminus1) Agricultural irrigation (A) Public-urban (B) Protection of aquatic life (C)

pd pm pd pm pd pmAl 1546 mdash mdash mdash mdash mdash mdashAs lt0098 02 04 01 02 01 02Cd lt0114 02 04 01 02 01 02Co 242 mdash mdash mdash mdash mdash mdashCulowast 689 40 60 40 60 40 60Crlowast 195 10 15 05 10 05 10Fe 1323 mdash mdash mdash mdash mdash mdashMn 723 mdash mdash mdash mdash mdash mdashCa 14887 mdash mdash mdash mdash mdash mdashMg 34 mdash mdash mdash mdash mdash mdashNa 19148 mdash mdash mdash mdash mdash mdashHglowast 007 001 002 0005 001 0005 001Nilowast 675 2 4 2 4 2 4Pblowast 123 05 1 02 04 02 04Zn 468 10 20 10 10 20 10V 024 mdash mdash mdash mdash mdash mdashMLA = maximum limits allowed pd = per day pm = per monthlowastValues that exceed the established MLA under Mexican Regulation

OH

CH3

CH3

(a)

OH

(b)

CH3

OH

(c)

OH

H3C

(d)

OH

CH3

(e)

Figure 3 Chemical structure of the main phenolic compounds identified by GC-MS in the spent caustics mixture (a) 24-dimethylphenol(b) phenol (c) m-methylphenol (d) p-methylphenol and (e) o-methylphenol

This analysis showed a uniform distribution of Ir (a1)

Ta (a2) Sn (b

1) B (c

1) and C (c

2) However the Sb in the

case of TiSnO2-Sb was not detected The absence of Sb was

probably due to the additive ratio in the coating solution Toverify its presence an XRD analysis was done demonstratingthe presence of SnO

2Sb2O3and Sb

2O5 For this specific

reason pretreatment of this electrode was performed beforethe cyclic voltammetric analysis At the same time for bothmaterials (TiIrO

2-Ta2O5and TiSnO

2-Sb) the wt of each

element was obtained by EDS In this analysis the presenceof additional elements such as O Ti and Si was detectedTheresults of these analyses (XRD and EDS) have been omitteddue to the formulation used In the case of TiBDD anexhaustive characterization was performed in other studies[94] The electrochemical characterization of each electrodeby CV is shown in Figure 4(d) It shows a comparativeanalysis of TiIrO

2-Ta2O5(d1) TiSnO

2-Sb (d

2) and TiBDD

(d3) in 05M H

2SO4 This graph shows that TiBDD has the

highest potential window in comparison to TiIrO2-Ta2O5

and TiSnO2-Sb An elevated 120578O

2is important taking into

account that the oxidation reaction of the organic compoundsduring the EO occurs in parallel to the evolution of O

2

Using a material with a high 120578O2 the oxidation reaction is

favored over the evolution of O2 resulting in high current

efficiencies Based on this it was decided that TiBDD wasthe best material to use in the electrochemical treatment ofspent caustic

322 Selection of the Reaction Medium To carry out theelectrochemical destruction of the spent caustics usingTiBDD the selection of the reaction medium was donetaking into account the following approaches (i) the pHeffecton the chemical state of phenol (ii) the pH effect on theTiBDDrsquos electrochemical response and (iii) the pH effect


minus2 minus1 0 1 2 3minus02

minus01

00

01

02

03

04

(d)

(c)

(b)

(a)

j(m

Acm

minus2 )

(a1) (a2)

(c1) (c2)

(b1)

(d1)

(d2)

(d3)

E(V) vs HgHg2SO4

Figure 4 SEM analysis (a) TiIrO2-Ta2O5 (b) TiSnO

2-Sb (c) TiBDD applying 15 kV with its respective micrographies and X-ray dot-

mapping analysis identifying (a1) Ir (a

2) Ta (b

1) Sn (c

1) B and (c

2) C (d) Cyclic voltammetry analysis for (d

1) TiIrO

2-Ta2O5 (d2) TiSnO

2-

Sb and (d3) TiBDD in 05M H

2SO4


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)

pH 1 pH 2 pH 3 pH 4 pH 5 pH 6

pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)

Figure 5 UV-Vis analysis of the pH effect on the chemical state of phenol using 30mg Lminus1 of TOC in (a) 005M NaOHH2SO4(pH 12ndash1)

(b) 005M NaOHHCl (pH 12ndash1) and (c) ORP analysis under the same conditions to 298K

on ∙OHs production According to the first approach in anextremely alkaline environment (pH 13ndash135 Table 1) thephenol is chemically transformed into sodium phenolates[90] Although the electronic state of phenol in an alkalinemedium has been shown to be favorable for an EO processusing electrodes with a low 120578O

2[28] this does not occur

using BDDwhere themost degradation efficiency is obtainedusing an acidic medium [90] Frequently in literature differ-ent types of acids have been reported for the EO of phenolsuch as HClO

4[63 104] and HNO

3[105] however for a

possible industrial application the costs of said acids must beconsidered For this reason and considering that during theion analysis a high quantity of chlorides (54900mg Lminus1) andsulfates (1882mg Lminus1) was identified as part of the chemical

composition of the spent caustics mixture HCl and H2SO4

were selected as possible acids to carry out the pH adjustment(13 135 to 1) Initially the acidification process was evaluatedusing a synthetic sample in order to rule out any chemicalchange that occurred on the phenolmolecule during the acid-ification process and to avoid an overestimation of the sub-sequent results In said analysis a solution of 005M NaOHcontaining phenol 30mg Lminus1 (TOC) was adjusted to differentpH values in an interval of 12ndash1 using 05MHCl and H

2SO4

The changes that occurred during the acidification pro-cess were evaluated through UV-Vis spectroscopy Figure 5shows the different UV-Vis absorption spectrums obtainedduring the adjustment of the pH using H

2SO4(Figure 5(a))

andHCl (Figure 5(b)) It is clearly observed that the chemical


0 1 2 3

000

004

008

012

minus2 minus1minus008

minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)

Figure 6 Electrochemical characterization of TiBDD by cyclic voltammetric analysis using (a1) 005M NaOHHCl (pH 1) and (a

2) 005M

NaOHH2SO4(pH 1) (b) ∙OHs analysis by fluorescence spectroscopy using (b

1) 005M NaOHHCl (pH 1) and (b

2) 005M NaOHH

2SO4

(pH 1) (c) Selection of the current density using synthetic solutions of phenol (30mg Lminus1 of TOC) in 005 NaOHH2SO4(pH 1)

conversion of sodium phenolates to phenol (120582 = 270 nm) isobtained with both types of acids at a pH of 9 reaching themaximum conversion efficiency at a pH of 7

There were no additional and significant chemicalchanges observed In parallel to this measurement an anal-ysis of the redox potential (ORP) was carried out at 298KThe result of this analysis is shown in Figure 5(c) The valuesobtained clearly show that an acidic pH favors highly oxi-dizing conditions which is of high importance consideringthat albeit an acidic environment does not alter the chemicalstructure of phenol the contaminants associated with thespent caustics can be liberated whereby a specialized infras-tructure and safety equipment are necessary Using H

2SO4

a slight increase in the ORP was observed in comparisonwith HCl which is logical considering a greater number ofprotons To evaluate the second approach (effect of the pH onthe electrochemical response of the TiBDD) different

voltammograms were obtained through the adjustment of005M NaOH with 05 H

2SO4and HCl in a pH range of 12ndash1

(data not shown) It was observed that when the pH valuesdescended to acidic the 120578O

2increased considerably [106]

When comparing the window of potential of H2SO4with that

of HCl (pH 1) (Figure 6(a)) a difference in overpotential of05 V was obtained Considering these results and accordingto the third approach (pH effect on ∙OHs production) ananalysis of the generation of the ∙OHs was carried out in bothreaction mediums (pH 1) Figure 6(b) shows the influence ofthe reaction medium on the production of ∙OHs It is clearlyobserved that the production of ∙OHs is greater in NaOHH2SO4(pH 1)

This result is of great importance considering thatwith the use of a BDD electrode the formation of anyoxidizing species produced in parallel to the oxidation oforganic compounds is strictly dependent on the formation of


0 2 4 6 8 10 1200

02

04

06

08

10

CODwithout lightTOCwithout lightCODwith light

TOCwith lightCODphotolysisTOCphotolysis

(a) (b) (c)

t (h)

CC

o

Figure 7 Evaluation of the use of UV light (120582 = 254 nm) Removal of COD and TOC in spent caustic corresponding to the simple sampleusing TiBDD applying 096A (119895 = 032A cmminus2) under constant stirring pH 1 (adjustment with H

2SO4) and 119905

119903= 12 h Images of (a) in the

absence of UV light (b) in the presence of UV light (120582 = 254 nm) and (c) photolysis

the ∙OHs Based on this result H2SO4was selected to carry

out the acidification process

323 Electrolysis Using TiBDD Before performing thedegradation experiments a preliminary analysis using asynthetic solution with a phenol concentration of 30mg Lminus1of TOC was carried out in NaOHH

2SO4(pH 1) with the

goal of identifying the current to be applied The currentsevaluated were 024 048 072 096 120 and 144A fora 2-hour period under constant stirring TiBDD (3 cm2)was used as anode and TiPt (3 cm2) was used as counter-electrode It was observed that the middle point of theremoval was reached at 096 A (119895 = 032A cmminus2) as shown inFigure 6(c) After having identified the current to be appliedand before carrying out electrolysis of the spent causticsmixture a preliminary electrolysis was performed using asimple sample (Table 1) The conditions of electrolysis were119895 = 032Acmminus2 pH 1 (adjustment with H

2SO4) In this anal-

ysis the effect of ultraviolet light was considered for thepurpose of favoring the synergic effect on the productionof the ∙OH It has been reported that in the presence ofchlorides the use of ultraviolet light (120582 = 254 nm) can leadto the production of the ∙OH according to the reaction (4)

HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)

Figure 7 shows the degradation profiles (TOC and COD)obtained in the different analyses done in the presence andabsence of UV light (120582 = 254 nm)

The results obtained in electrolysis in the absence of lightwere more satisfactory than those obtained in its presence(120582 = 254 nm) The results obtained can be attributed to thetype of sample analyzed A real sample is not comparable toa synthetic sample Here it is inferred that due to the high

content of organic material oxidation processes differentfrom those that occurred in the interface or by the action ofthe oxidants themselves are not significant When analyzingthe effect of UV light (120582 = 254 nm) without applying acurrent (photolysis) no significant change was observed

Figure 8 shows the analysis of images obtained during thedifferent electrolysis carried out

The initial image (119905119903= 0 h) corresponds to the simple

sample submitted to a special pretreatment before electrolysis(acidification to pH 1 using H

2SO4) A dark brown color

in the first stages of the phenol electrolysis is related tothe formation of byproducts such as benzoquinone andhydroquinone known as an active redox couple in equi-librium in an aqueous solution [51] The color degradationin each experiment was gradual When comparing eachimage (119905

119903= 8 h) it is clearly observed that in electrolysis

carried out in the absence of light (Figure 8(a)) the sampleturned completely crystalline indicating a high level ofdestruction of the organic content Contrarily in electrolysisin the presence of light (120582 = 254 nm) (Figure 8(b)) andin photolysis experiments (Figure 8(c)) the opposite processwas observed In the presence of light (120582 = 254 nm) thedegradation time to obtain a visually crystalline sample wasgreater (119905

119903= 12 h) Based on these results the use of UV

light (120582 = 254 nm) was discarded On the other hand andconsidering the results obtained the possible passivation ofTiBDD as an important point was also evaluated In thisanalysis the ∙OHs production was performed in function ofthe interfacial potential or current applied The result (datanot shown) indicates that these species only are generated inthe zone corresponding to the decomposition of themediumwhereby if the domains of the potential or current appliedare not the correct ones the electrode can be completely


8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)

Figure 8 Images of electrolysis of spent caustic corresponding to the simple sample (a) In the absence of UV light (b) In the presence of UVlight (120582 = 254 nm) (c) Photolysis using TiBDD applying 096A (119895 = 032Acmminus2) under constant stirring pH 1 (adjustment with H

2SO4)

and 119905119903= 12 h

Table 3 Electrochemical treatment of spent caustics (mixture) using TiBDD

Sample COD(mg Lminus1)

COD removal()

Total removalefficiency WT-ET ()

TOC(mg Lminus1)

TOC removal()


Without treatment (WT) 98750 0 mdash 201375 0 0Chemical treatment (CT)lowast 24533 7515 mdash 15700 2203 mdashElectrochemical treatment (ET) 2333 9040 9663 2322 8521 8846lowastAcidification to pH 1 using H2SO4

passivated The image analysis of this test is shown inFigure 9 As can be observed (Figure 9(a)) when workingwith a current where the production of the ∙OHs doesnot occur a thick layer of organic compounds is depositedcausing the deactivation of the electrode

Contrarily when the current is applied inducing a greaterinterfacial potential by which ∙OHs are electrogenerated theTiBDD electrode can be operated successfully (Figure 9(b))Finally and according to the previous studies the electrolysisof the mixture (100mL) of spent caustics was carried out

(pH 1H2SO4 119895 = 032A cmminus2) The results obtained in this

analysis are shown in Table 3 The results obtained weresimilar to those from electrolysis of the simple sample

The analysis of the image of the sample correspondingto the mixture of spent caustics before and after the elec-trochemical treatment with TiBDD (119905

119903= 15 h) is shown

in Figures 9(c) and 9(d) respectively Complementary anal-yses of toxicity and phenol in all of its forms showed thatthe sample electrochemically treated is not toxic present-ing a low phenol content (lt3 ppm) with this value being


(a) (b)

(c) (d)

Figure 9 Electrochemical treatment of spent caustics mixture (a) Applying a current where the ∙OHs are not generated (b) Applyinga current where the ∙OHs are generated (c) Electrolyzed sample (without pretreatment) (d) Sample obtained after the electrochemicaltreatment with TiBDD applying 096A (119895 = 032Acmminus2) under constant stirring pH 1 (adjustment with H

2SO4) and 119905

119903= 15 h

the minimum standard discharge limit for refinery effluents[107]

4 Conclusions

A greater production of the ∙OH was obtained by usingH2SO4as a reaction medium The degradation of spent

caustics in an acidic medium (H2SO4 pH 1) using TiBDD in

simple samples proceeded at 100while for themixture per-centages of destruction of 9040 and 8521 for COD andTOC respectively were obtained The use of UV light (120582 =254 nm)did not showan improvement of the process Furtherstudies are necessary to improve the efficiencies obtained

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thankMexicorsquos National Council ofScience andTechnology (CONACyT) for its financial supportof this research The authors also thank Ms Alejandra Rojo(native speaker) for her review of this paper

References

[1] I Hariz A Halleb N Adhoum and L Monser ldquoTreatment ofpetroleum refinery sulfidic spent caustic wastes by electroco-agulationrdquo Separation and Purification Technology vol 107 pp150ndash157 2013

[2] S-H Sheu and H-S Weng ldquoTreatment of olefin plant spentcaustic by combination of neutralization and fenton reactionrdquoWater Research vol 35 no 8 pp 2017ndash2021 2001

[3] A Olmos P Olguin C Fajardo E Razo and O MonroyldquoPhysicochemical characterization of spent caustic from the


OXIMER process and sour waters from mexican oil refineriesrdquoEnergy amp Fuels vol 18 no 2 pp 302ndash304 2004

[4] H Jiang Y Fang Y Fu and Q-X Guo ldquoStudies on theextraction of phenol in wastewaterrdquo Journal of HazardousMaterials vol 101 no 2 pp 179ndash190 2003

[5] Y Han X Quan S Chen H Zhao C Cui and Y ZhaoldquoElectrochemically enhanced adsorption of phenol on activatedcarbon fibers in basic aqueous solutionrdquo Journal of Colloid andInterface Science vol 299 no 2 pp 766ndash771 2006

[6] A Nuhoglu and B Yalcin ldquoModelling of phenol removal in abatch reactorrdquo Process Biochemistry vol 40 no 3-4 pp 1233ndash1239 2005

[7] D Rajkumar and K Palanivelu ldquoElectrochemical treatment ofindustrial wastewaterrdquo Journal of Hazardous Materials vol 113no 1ndash3 pp 123ndash129 2004

[8] H Polat M Molva and M Polat ldquoCapacity and mechanism ofphenol adsorption on ligniterdquo International Journal of MineralProcessing vol 79 no 4 pp 264ndash273 2006

[9] Y Yavuz A S Koparal and U B Ogutveren ldquoTreatment ofpetroleum refinery wastewater by electrochemical methodsrdquoDesalination vol 258 no 1ndash3 pp 201ndash205 2010

[10] H Farajnezhad and P Gharbani ldquoCoagulation treatment ofwastewater in petroleum industry using poly aluminum chlo-ride and ferric chloriderdquo International Journal of Research andReviews in Applied Sciences vol 13 no 1 pp 306ndash310 2012

[11] L Altas and H Buyukgungor ldquoSulfide removal in petroleumrefinery wastewater by chemical precipitationrdquo Journal of Haz-ardous Materials vol 153 no 1-2 pp 462ndash469 2008

[12] C E Santo V J P Vilar C M S Botelho A Bhatnagar EKumar and R A R Boaventura ldquoOptimization of coagulation-flocculation and flotation parameters for the treatment of apetroleum refinery effluent from a Portuguese plantrdquo ChemicalEngineering Journal vol 183 pp 117ndash123 2012

[13] M H El-Naas S Al-Zuhair A Al-Lobaney and S MakhloufldquoAssessment of electrocoagulation for the treatment ofpetroleum refinery wastewaterrdquo Journal of EnvironmentalManagement vol 91 no 1 pp 180ndash185 2009

[14] C-L Yang ldquoElectrochemical coagulation for oily water demul-sificationrdquo Separation and Purification Technology vol 54 no3 pp 388ndash395 2007

[15] M A Zazouli M Taghavi and E Bazrafshan ldquoInfluences ofsolution chemistry on phenol removal from aqueous environ-ments by electrocoagulation process using aluminium elec-trodesrdquo Journal of Health Scope vol 1 no 2 pp 66ndash70 2012

[16] O Abdelwahab N K Amin and E-S Z El-Ashtoukhy ldquoElec-trochemical removal of phenol from oil refinery wastewaterrdquoJournal of Hazardous Materials vol 163 no 2-3 pp 711ndash7162009

[17] A Dimoglo H Y Akbulut F Cihan and M KarpuzculdquoPetrochemical wastewater treatment bymeans of clean electro-chemical technologiesrdquo Clean Technologies and EnvironmentalPolicy vol 6 no 4 pp 288ndash295 2004

[18] M H El-Naas M A Alhaija and S Al-Zuhair ldquoEvaluationof a three-step process for the treatment of petroleum refinerywastewaterrdquo Journal of Environmental Chemical Engineeringvol 2 no 1 pp 56ndash62 2014

[19] A Coelho A V Castro M Dezotti and G L SantrsquoAnna JrldquoTreatment of petroleum refinery sourwater by advanced oxi-dation processesrdquo Journal of Hazardous Materials vol 137 no1 pp 178ndash184 2006

[20] G Salas and N Ale ldquoTreatment of wastewaters from apretroleum refinery through advanced oxidation (AOX) usingreactive Fenton (H

2O2Fe2+)rdquo Peruvian Magazine of Chemistry

and Chemical Engineering vol 11 no 2 pp 12ndash18 2008[21] S Sayid M Abu Z Noor S Noor and A Aris ldquoFenton and

photo-fenton oxidation of sulfidic spent caustic a comparativestudy based on statistical analysisrdquo Environmental Engineeringand Management Journal vol 13 no 3 pp 531ndash538 2014

[22] C Comninellis ldquoElectrocatalysis in the electrochemical con-versioncombustion of organic pollutants for waste water treat-mentrdquoElectrochimicaActa vol 39 no 11-12 pp 1857ndash1862 1994

[23] V S de Sucre and A PWatkinson ldquoAnodic oxidation of phenolfor waste water treatmentrdquo The Canadian Journal of ChemicalEngineering vol 59 no 1 pp 52ndash59 1981

[24] B Fleszar and J Poszynska ldquoAn attempt to define benzene andphenol electrochemical oxidation mechanismrdquo ElectrochimicaActa vol 30 no 1 pp 31ndash42 1985

[25] H Sharifian and D W Kirk ldquoElectrochemical oxidation ofphenolrdquo Journal of the Electrochemical Society vol 113 no 5 pp921ndash924 1986

[26] I F McConvey K Scott J M Henderson and A N HainesldquoElectrochemical reaction with parallel reversible surfaceadsorption interpretations of the kinetics of anodic oxidationof aniline and phenol to carbon dioxiderdquo Chemical Engineeringand Processing Process Intensification vol 22 no 4 pp 231ndash2351987

[27] D-T Chin N R K Vilambi and C Y Cheng ldquoOxidation ofphenol to benzoquinone in a CSTER with modulated alter-nating voltagerdquo Journal of Applied Electrochemistry vol 19 no3 pp 459ndash461 1989

[28] C Comninellis and C Pulgarin ldquoAnodic oxidation of phenolfor waste water treatmentrdquo Journal of Applied Electrochemistryvol 21 no 8 pp 703ndash708 1991

[29] R Kotz S Stucki and B Carcer ldquoElectrochemical waste watertreatment using high overvoltage anodes Part I physical andelectrochemical properties of SnO

2anodesrdquo Journal of Applied

Electrochemistry vol 21 no 1 pp 14ndash20 1991[30] S Stucki R Kotz B Carcer and W Suter ldquoElectrochemical

waste water treatment using high overvoltage anodes PartII anode performance and applicationsrdquo Journal of AppliedElectrochemistry vol 21 no 2 pp 99ndash104 1991

[31] O J Murphy G D Hitchens L Kaba and C E VerostkoldquoDirect electrochemical oxidation of organics for wastewatertreatmentrdquoWater Research vol 26 no 4 pp 443ndash451 1992

[32] C Comninellis and C Pulgarin ldquoElectrochemical oxidation ofphenol for wastewater treatment using SnO

2 anodesrdquo Journal

of Applied Electrochemistry vol 23 no 2 pp 108ndash112 1993[33] K T Kawagoe and D C Johnson ldquoElectrocatalysis of anodic

oxygen-transfer reactions Oxidation of phenol and benzeneat bismuth-doped lead dioxide electrodes in acidic solutionsrdquoJournal of the Electrochemical Society vol 141 no 12 pp 3404ndash3409 1994

[34] C Comninellis and A Nerini ldquoAnodic oxidation of phenolin the presence of NaCl for wastewater treatmentrdquo Journal ofApplied Electrochemistry vol 25 no 1 pp 23ndash28 1995

[35] N B Tahar and A Savall ldquoMechanistic aspects of phenolelectrochemical degradation by oxidation on a TaPbO

2anoderdquo

Journal of the Electrochemical Society vol 145 no 10 pp 3427ndash3434 1998

[36] U Schumann and P Grundler ldquoElectrochemical degradation oforganic substances at PbO

2anodes monitoring by continuous


CO2measurementsrdquo Water Research vol 32 no 9 pp 2835ndash

2842 1998[37] N B Tahar and A Savall ldquoElectrochemical degradation of

phenol in aqueous solution on bismuth doped lead dioxide acomparison of the activities of various electrode formulationsrdquoJournal of Applied Electrochemistry vol 29 no 3 pp 277ndash2831999

[38] P Canizares J A Domınguez M A Rodrigo J Villasenor andJ Rodrıguez ldquoEffect of the current intensity in the electrochem-ical oxidation of aqueous phenol wastes at an activated carbonand steel anoderdquo Industrial amp Engineering Chemistry Researchvol 38 no 10 pp 3779ndash3785 1999

[39] J Iniesta J Gonzalez-Garcıa E Exposito V Montiel and AAldaz ldquoInfluence of chloride ion on electrochemical degrada-tion of phenol in alkaline medium using bismuth doped andpure PbO

2anodesrdquo Water Research vol 35 no 14 pp 3291ndash

3300 2001[40] G A Bogdanovskii T V Savelrsquoeva and T S Saburova ldquoPhenol

conversions during electrochemical generation of active chlo-rinerdquo Russian Journal of Electrochemistry vol 37 no 8 pp 865ndash869 2001

[41] ZWu andM Zhou ldquoPartial degradation of phenol by advancedelectrochemical oxidation processrdquo Environmental Science andTechnology vol 35 no 13 pp 2698ndash2703 2001

[42] MH Zhou Z CWu andDHWang ldquoA novel electrocatalysismethod for organic pollutants degradationrdquo Chinese ChemicalLetters vol 12 no 10 pp 929ndash932 2001

[43] R T Pelegrini R S Freire N Duran and R Bertazzoli ldquoPho-toassisted electrochemical degradation of organic pollutants ona DSA type oxide electrode process test for a phenol syntheticsolution and its application for the E1 bleach Kraftmill effluentrdquoEnvironmental Science and Technology vol 35 no 13 pp 2849ndash2853 2001

[44] M-H Zhou Z-C Wu and X-D Xuan ldquoAnodic-cathodicelectrocatalytic degradation of phenol with oxygen spargedin the presence of iron (II)rdquo Chemical Research in ChineseUniversities vol 18 no 3 pp 262ndash266 2002

[45] R L Pelegrino R A Di Iglia C G Sanches L A Avaca and RBertazzoli ldquoComparative study of commercial oxide electrodesperformance in electrochemical degradation of organics inaqueous solutionsrdquo Journal of the Brazilian Chemical Societyvol 13 no 1 pp 60ndash65 2002

[46] Y J Feng and X Y Li ldquoElectro-catalytic oxidation of phenolon several metal-oxide electrodes in aqueous solutionrdquo WaterResearch vol 37 no 10 pp 2399ndash2407 2003

[47] P D P Alves M Spagnol G Tremiliosi-Filho and A R deAndrade ldquoInvestigation of the influence of the anode compo-sition of DSA-type electrodes on the electrocatalytic oxidationof phenol in neutral mediumrdquo Journal of the Brazilian ChemicalSociety vol 15 no 5 pp 626ndash634 2004

[48] P Canizares J Garcıa-Gomez J Lobato and M A RodrigoldquoModeling of wastewater electro-oxidation processes part IGeneral description and application to inactive electrodesrdquoIndustrial amp Engineering Chemistry Research vol 43 no 9 pp1915ndash1922 2004

[49] P Canizares J Garcıa-Gomez J Lobato and M A RodrigoldquoModeling of wastewater electro-oxidation processes part IIApplication to active electrodesrdquo Industrial amp EngineeringChemistry Research vol 43 no 9 pp 1923ndash1931 2004

[50] D Fino C C Jara G Saracco V Specchia and P SpinellildquoDeactivation and regeneration of Pt anodes for the electro-oxidation of phenolrdquo Journal of Applied Electrochemistry vol35 no 4 pp 405ndash411 2005

[51] X-Y Li Y-H Cui Y-J Feng Z-M Xie and J-D Gu ldquoReactionpathways and mechanisms of the electrochemical degradationof phenol on different electrodesrdquo Water Research vol 39 no10 pp 1972ndash1981 2005

[52] M Li C FengWHu Z Zhang andN Sugiura ldquoElectrochem-ical degradation of phenol using electrodes of TiRuO

2-Pt and

TiIrO2-Ptrdquo Journal of Hazardous Materials vol 162 no 1 pp

455ndash462 2009[53] E Chatzisymeon S Ferro I Karafyllis D Mantzavinos N

Kalogerakis andA Katsaounis ldquoAnodic oxidation of phenol onTiIrO

2electrode experimental studiesrdquo Catalysis Today vol

151 no 1-2 pp 185ndash189 2010[54] Y Yavuz and A S Koparal ldquoElectrochemical oxidation of

phenol in a parallel plate reactor using ruthenium mixed metaloxide electroderdquo Journal of Hazardous Materials vol 136 no 2pp 296ndash302 2006

[55] A M Z Ramalho C A Martınez-Huitle and D R DSilva ldquoApplication of electrochemical technology for removingpetroleum hydrocarbons from produced water using a DSA-type anode at different flow ratesrdquo Fuel vol 89 no 2 pp 531ndash534 2010

[56] M R G Santos M O F Goulart J Tonholo and C L P SZanta ldquoThe application of electrochemical technology to theremediation of oily wastewaterrdquoChemosphere vol 64 no 3 pp393ndash399 2006

[57] F Montilla E Morallon and J L Vazquez ldquoEvaluation of theelectrocatalytic activity of antimony-doped tin dioxide anodestoward the oxidation of phenol in aqueous solutionsrdquo Journal ofthe Electrochemical Society vol 152 no 10 pp B421ndashB427 2005

[58] Z-C Wu M-H Zhou Z-W Huang and D-H Wang ldquoElec-trocatalysis method for wastewater treatment using a novelbeta-lead dioxide anoderdquo Journal of Zhejinag University Sciencevol 3 no 2 pp 194ndash198 2002

[59] M Zhou Q Dai L Lei C Ma and D Wang ldquoLong lifemodified lead dioxide anode for organic wastewater treatmentelectrochemical characteristics and degradation mechanismrdquoEnvironmental Science and Technology vol 39 no 1 pp 363ndash370 2005

[60] P-AMichaudM Panizza L Ouattara T Diaco G Foti andCComninellis ldquoElectrochemical oxidation of water on syntheticboron-doped diamond thin film anodesrdquo Journal of AppliedElectrochemistry vol 33 no 2 pp 151ndash154 2003

[61] A Kraft M Stadelmann and M Blaschke ldquoAnodic oxidationwith doped diamond electrodes a new advanced oxidationprocessrdquo Journal of HazardousMaterials vol 103 no 3 pp 247ndash261 2003

[62] B Marselli J Garcıa-Gomez P-A Michaud M A Rodrigoand C Comninellis ldquoElectrogeneration of hydroxyl radicals onboron-doped diamond electrodesrdquo Journal of the Electrochemi-cal Society vol 150 no 3 pp D79ndashD83 2003

[63] J Iniesta P A Michaud M Panizza G Cerisola A Aldaz andC Comninellis ldquoElectrochemical oxidation of phenol at boron-doped diamond electroderdquo Electrochimica Acta vol 46 no 23pp 3573ndash3578 2001

[64] M Panizza P A Michaud G Cerisola and C ComninellisldquoElectrochemical treatment of wastewaters containing organicpollutants on boron-doped diamond electrodes prediction


of specific energy consumption and required electrode areardquoElectrochemistry Communications vol 3 no 7 pp 336ndash3392001

[65] P L Hagans P M Natishan B R Stoner and W E OrsquoGradyldquoElectrochemical oxidation of phenol using boron-doped dia-mond electrodesrdquo Journal of the Electrochemical Society vol148 no 7 pp E298ndashE301 2001

[66] P Canizares M Dıaz J A Domınguez J Garcıa-Gomez andM A Rodrigo ldquoElectrochemical oxidation of aqueous phenolwastes on synthetic diamond thin-film electrodesrdquo Industrial ampEngineering Chemistry Research vol 41 no 17 pp 4187ndash41942002

[67] A V Diniz N G Ferreira E J Corat and V J Trava-AiroldildquoEfficiency study of perforated diamond electrodes for organiccompounds oxidation processrdquoDiamond andRelatedMaterialsvol 12 no 3ndash7 pp 577ndash582 2003

[68] J-F Zhi H-B Wang T Nakashima T N Rao and AFujishima ldquoElectrochemical incineration of organic pollutantson boron-doped diamond electrode evidence for direct electro-chemical oxidation pathwayrdquoThe Journal of Physical ChemistryB vol 107 no 48 pp 13389ndash13395 2003

[69] A M Polcaro A Vacca S Palmas and M Mascia ldquoElectro-chemical treatment of wastewater containing phenolic com-pounds oxidation at boron-doped diamond electrodesrdquo Jour-nal of Applied Electrochemistry vol 33 no 10 pp 885ndash892 2003

[70] P Canizares J Garcıa-Gomez C Saez and M A RodrigoldquoElectrochemical oxidation of several chlorophenols on dia-mond electrodes Part I Reaction mechanismrdquo Journal ofApplied Electrochemistry vol 33 no 10 pp 917ndash927 2003

[71] P Canizares J Garcıa-Gomez J Lobato and M A RodrigoldquoElectrochemical oxidation of aqueous carboxylic acid wastesusing diamond thin-film electrodesrdquo Industrial amp EngineeringChemistry Research vol 42 no 5 pp 956ndash962 2003

[72] A Morao A Lopes M T P de Amorim and I C GoncalvesldquoDegradation of mixtures of phenols using boron dopeddiamond electrodes for wastewater treatmentrdquo ElectrochimicaActa vol 49 no 9-10 pp 1587ndash1595 2004

[73] P Canizares C Saez J Lobato and M A Rodrigo ldquoElectro-chemical oxidation of polyhydroxybenzenes on boron-dopeddiamond anodesrdquo Industrial amp Engineering Chemistry Researchvol 43 no 21 pp 6629ndash6637 2004

[74] P Canizares J Lobato R Paz M A Rodrigo and C SaezldquoElectrochemical oxidation of phenolic wastes with boron-doped diamond anodesrdquo Water Research vol 39 no 12 pp2687ndash2703 2005

[75] C Flox J A Garrido R M Rodrıguez et al ldquoDegradationof 46-dinitro-o-cresol from water by anodic oxidation with aboron-doped diamond electroderdquo Electrochimica Acta vol 50no 18 pp 3685ndash3692 2005

[76] M J Pacheco A Morao A Lopes L Cirıaco and I GoncalvesldquoDegradation of phenols using boron-doped diamond elec-trodes a method for quantifying the extent of combustionrdquoElectrochimica Acta vol 53 no 2 pp 629ndash636 2007

[77] M Mascia A Vacca S Palmas and A M Polcaro ldquoKinetics ofthe electrochemical oxidation of organic compounds at BDDanodes modelling of surface reactionsrdquo Journal of AppliedElectrochemistry vol 37 no 1 pp 71ndash76 2007

[78] X Zhu S Shi J Wei et al ldquoElectrochemical oxidation charac-teristics of p-substituted phenols using a boron-doped diamondelectroderdquo Environmental Science and Technology vol 41 no 18pp 6541ndash6546 2007

[79] C Flox P-L Cabot F Centellas et al ldquoSolar photoelectro-Fenton degradation of cresols using a flow reactor with a boron-doped diamond anoderdquoApplied Catalysis B Environmental vol75 no 1-2 pp 17ndash28 2007

[80] M Mascia A Vacca A M Polcaro S Palmas J R Ruiz andA da Pozzo ldquoElectrochemical treatment of phenolic watersin presence of chloride with boron-doped diamond (BDD)anodes experimental study and mathematical modelrdquo Journalof Hazardous Materials vol 174 no 1ndash3 pp 314ndash322 2010

[81] X Zhu J Ni H Li Y Jiang X Xing and A G L BorthwickldquoEffects of ultrasound on electrochemical oxidation mecha-nisms of p-substituted phenols at BDD and PbO

2anodesrdquo

Electrochimica Acta vol 55 no 20 pp 5569ndash5575 2010[82] X Zhu J Ni J Wei X Xing H Li and Y Jiang ldquoScale-up

of BDD anode system for electrochemical oxidation of phenolsimulated wastewater in continuous moderdquo Journal of Haz-ardous Materials vol 184 no 1ndash3 pp 493ndash498 2010

[83] J Wei X Zhu and J Ni ldquoElectrochemical oxidation of phenolat boron-doped diamond electrode in pulse current moderdquoElectrochimica Acta vol 56 no 15 pp 5310ndash5315 2011

[84] J Sun H Lu H Lin et al ldquoElectrochemical oxidation ofaqueous phenol at low concentration using TiBDD electroderdquoSeparation and Purification Technology vol 88 pp 116ndash1202012

[85] J Lv Y Feng J Liu Y Qu and F Cui ldquoComparison ofelectrocatalytic characterization of boron-doped diamond andSnO2electrodesrdquoApplied Surface Science vol 283 pp 900ndash905

2013[86] G Hurwitz P Pornwongthong S Mahendra and E M

V Hoek ldquoDegradation of phenol by synergistic chlorine-enhanced photo-assisted electrochemical oxidationrdquo ChemicalEngineering Journal vol 240 pp 235ndash243 2014

[87] X Chen G Chen F Gao and P L Yue ldquoHigh-performanceTiBDD electrodes for pollutant oxidationrdquo EnvironmentalScience and Technology vol 37 no 21 pp 5021ndash5026 2003

[88] X Chen F Gao and G Chen ldquoComparison of TiBDD andTiSnO

2-Sb2O5electrodes for pollutant oxidationrdquo Journal of

Applied Electrochemistry vol 35 no 2 pp 185ndash191 2005[89] E Weiss K Groenen-Serrano and A Savall ldquoA comparison

of electrochemical degradation of phenol on boron dopeddiamond and lead dioxide anodesrdquo Journal of Applied Electro-chemistry vol 38 no 3 pp 329ndash337 2008

[90] A Medel E Bustos K Esquivel L A Godınez and Y MeasldquoElectrochemical incineration of phenolic compounds from thehydrocarbon industry using boron-doped diamond electrodesrdquoInternational Journal of Photoenergy vol 2012 Article ID681875 6 pages 2012

[91] J H Bezerra M M Soares N Suely D Riveiro and C AMartınez-Huitle ldquoApplication of electrochemical oxidation asalternative treatment of produced water generated by Brazilianpetrochemical industryrdquo Fuel vol 96 pp 80ndash87 2012

[92] A J C da Silva E V dos Santos C C D O MoraisC A Martınez-Huitle and S S L Castro ldquoElectrochemicaltreatment of fresh brine and saline produced water generatedby petrochemical industry using TiIrO

2-Ta2O5and BDD in

flow reactorrdquo Chemical Engineering Journal vol 233 pp 47ndash552013

[93] R B A Souza and L AM Ruotolo ldquoElectrochemical treatmentof oil refinery effluent using boron-doped diamond anodesrdquoJournal of Environmental Chemical Engineering vol 1 no 3 pp544ndash551 2013


[94] A Medel E Bustos L M Apatiga and Y Meas ldquoSurfaceactivation of C-sp3 in Boron-Doped diamond electroderdquo Elec-trocatalysis vol 4 no 4 pp 189ndash195 2013

[95] Mexican Regulation NMX-AA-050-SCFI-2001 ldquoAnalysis ofwater-determination of total phenols in natural potable resid-ual and treated residual watersrdquo 2001

[96] A Fakhrursquol-Razi A Pendashteh L C Abdullah D R A BiakS S Madaeni and Z Z Abidin ldquoReview of technologies foroil and gas produced water treatmentrdquo Journal of HazardousMaterials vol 170 no 2-3 pp 530ndash551 2009

[97] L Wei S Guo G Yan C Chen and X Jiang ldquoElectrochemicalpretreatment of heavy oil refinery wastewater using a three-dimensional electrode reactorrdquo Electrochimica Acta vol 55 no28 pp 8615ndash8620 2010

[98] E V dos Santos S F M Sena D R da Silva S Ferro A de Bat-tisti and C A Martınez-Huitle ldquoScale-up of electrochemicaloxidation system for treatment of produced water generated byBrazilian petrochemical industryrdquo Environmental Science andPollution Research vol 21 pp 8466ndash8475 2014

[99] M Murugananthan S S Latha G B Raju and S YoshiharaldquoRole of electrolyte on anodic mineralization of atenolol atboron doped diamond and Pt electrodesrdquo Separation andPurification Technology vol 79 no 1 pp 56ndash62 2011

[100] A Sanchez-Carretero C Saez P Canizares andM A RodrigoldquoElectrochemical production of perchlorates using conductivediamond electrolysesrdquo Chemical Engineering Journal vol 166no 2 pp 710ndash714 2011

[101] Official Mexican Regulation NOM-001-SEMARNAT-1996ldquoMaximum limits allowed of pollutants in discharges ofwastewaters and national resourcesrdquo 1996

[102] B F GiannettiWAMoreira SH Bonilla CMV B Almeidaand T Raboczkay ldquoTowards the abatement of environmentalmercury pollution an electrochemical characterizationrdquo Col-loids and Surfaces A Physicochemical and Engineering Aspectsvol 276 no 1ndash3 pp 213ndash220 2006

[103] U Skyllberg P R Bloom J Qian C-M Lin and W FBleam ldquoComplexation of mercury(II) in soil organic matterEXAFS evidence for linear two-coordination with reducedsulfur groupsrdquo Environmental Science and Technology vol 40no 13 pp 4174ndash4180 2006

[104] D T Cestarolli and A R de Andrade ldquoElectrochemical oxida-tion of phenol at TiRu

03Pb(07minusx)TixOy electrodes in aqueous

mediardquo Journal of the Electrochemical Society vol 154 no 2 ppE25ndashE30 2007

[105] S Balaji S J Chung R Thiruvenkatachari and I S MoonldquoMediated electrochemical oxidation process electro-oxidationof cerium(III) to cerium(IV) in nitric acid medium and astudy on phenol degradation by cerium(IV) oxidantrdquo ChemicalEngineering Journal vol 126 no 1 pp 51ndash57 2007

[106] D Reyter D Belanger and L Roue ldquoNitrate removal by apaired electrolysis on copper and TiIrO

2coupled electrodesmdash

influence of the anodecathode surface area ratiordquo WaterResearch vol 44 no 6 pp 1918ndash1926 2010

[107] B H DiyarsquoUddeen W M A W Daud and A R Abdul AzizldquoTreatment technologies for petroleum refinery effluents areviewrdquo Process Safety and Environmental Protection vol 89 no2 pp 95ndash105 2011

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


others [1] which require unconventional handling and treat-ment due to their highly toxic nature and unpleasant odor(the mercaptans can be detected in ppb) In the specific caseof spent caustics produced from olefins plants large amountsof S2minus (14000ndash21000mg Lminus1) pH values of 135 to 137 andemulsified hydrocarbons have also been reported [2] Withregard to the phenolic content depending on the refiningprocess it can reach up to 30600mg Lminus1 [3] The potentialdanger of the spent caustics can be understood consideringthe fact that by not having technology for its treatment insitu the different types of spent caustics can be combinedresulting in the production of highly toxic mixtures On theother hand when the spent caustics are not treated immedi-ately these are temporarily stored or confined by authorizedcompanies with their transport and storage being a latentthreat due to the possibility of spillage which has alreadybeen recorded in history with a highly negative impact onhuman health A concentration of phenol ranging from 5to 25mg Lminus1 is as toxic for aquatic life as it is for humans[4 5] For this reason the maximum limits allowed of phenolresidues found in industrial discharges vary between 05 and10mg Lminus1 [5] In the case of potable drinking water theEuropean Union (EU) in its 80778EC Directive assigned amaximum limit allowed oflt00005mg Lminus1 for phenol in all ofits forms [4] given that the consumption of water containingthese compounds can induce cancer or death [6] At the sametime the elevated danger of this contaminant for aquaticlife has marked phenol and some phenolic compounds aspriority contaminants in agreement with the criteria of theEnvironmental Protection Agency (EPA) of the United States[4 5] In a conventional manner the treatment of spentcaustics from refineries has been carried out in three steps(1) wet air oxidation (WAO) (2) acid neutralization (AN)and (3) biological oxidation (BO) On occasions step (2)can be followed by steam stripping After AN strippingremoves residual H

2S and mercaptans The liquid effluent

obtained has high BOD and COD concentrations becausethe major portion of the organic constituents is unaffected bythe stripping process Although WAO can treat spent causticto lower than 1000mg Lminus1 COD in 60min at 475K and 28bar the process is very expensive and due to severe reactionconditions safety is a major concern [2] At the same timethough the elimination of contaminants in steps (1) and (2)can lead to the obtainment of wastewater easily treatableby BO this depends strictly on the level of conversion andremoval of the contaminants found For example if the sulfurcontent is high and the concentration of phenols is low theBO (use of bacteria from the genus Thiobacillus) is possibleContrarily the process can be deactivated when the concen-tration of phenol is high It has been reported that effluentscontaining phenol with a concentration of gt3000mg Lminus1cannot be treated through BO [4] Taking this problem intoaccount different processes have been applied and evaluatedfor the treatment of effluents from refineries leaving asidethe treatment of the spent caustics It is important to mentionthat the physicochemical nature and composition of the spentcaustics is not comparable to wastewater produced as partof the extraction processes of crude oil (water produced)

or the wastewater produced in other processes In spentcaustics the content of phenolic compounds can reach avalue of 30600mg Lminus1 [3] while in water produced or anyother kind of wastewater this value can oscillate between20 and 200mg Lminus1 [7ndash9] In the case of wastewaters fromrefineries the chemical coagulation using polyaluminiumchloride [10] chemical precipitation [11] integrated processes(coagulation-flocculation and flotation) [12] and electroco-agulation (EC) has been reported to remove the high contentof the organic material found [13] At the same time andconsidering the importance of the phenolic content as wellas the content of commonly found fats and oils [14] theEC has also been evaluated using NaCl reaching removalpercentages of 91 [15] and 945 [16] for synthetic and realsamples respectively In other studies the combination ofelectroflotation (EF) and EC and integrated processes (EC-adsorption-BO) have also been proposed [17 18] Althoughin spent caustics the EC has been tested for the removal ofsulfides and organic material [1] it is important to highlightthat the nature of this process is not destructive allowing thetransference of the pollutants from one phase to another withthe subsequent disposal problemOn the other hand and con-sidering the technical difficulties in treating aqueous wastescontaining phenol or phenolic compounds through WAOBO or EC alternative processes of a destructive nature suchas the chemical advanced oxidation processes (AOPs in thepresence or absence of sunlight or assisted light) like theuse of hydrogen peroxide (H

2O2) ozone (O

3) photocatalysis

Fenton process and the ozonation in alkaline medium havebeen amply tested in the treatment of phenols and phenoliccompounds However the majority of these studies haveonly been carried out on synthetic samples In real samplesfrom refineries applying these processes only a few studieshave been reported [19]Considering the importance impliedin the treatment of real samples in the last years (2000ndash2014) different isolated studies have been reported on thetreatment of spent caustics using the Fenton process In thissense samples containing a COD of 20160mg Lminus1 and atotal of phenols of 1800mg Lminus1 have been successfully treatedobtaining removal efficiencies of 90 for COD and 99 fortotal phenols at a pH of 4 [20] At the same time whencomparing this process using assisted light (photo-Fenton)in the treatment of sulfidic spent caustics a greater efficiencywas reached with a removal of COD and sulfide up to 97and 100 respectively [21] Applying both processes anddespite the excellent results in practice the percentage oftotal destruction of the organic content is strictly dependenton the physicochemical composition of the sample to betreated An elevated organic charge consumes a large amountof H2O2 Also because of a high concentration of H

2S (up

to 20 g Lminus1) its reaction with ferric ion causes a loss ofiron catalyst activity [2] At the same time it is necessaryto emphasize that the chemical AOPs do not possess theability to destroy the reaction byproducts Contrarily oneof the most efficient processes and with the potential tocarry out the destruction of any contaminant including phe-nol and phenolic compounds is electrochemical oxidation(EO) Said technology bases its efficiency on the nature of



2 TiRuO



2-Sb


2andwater due to


2)






2-



3 H2O2 and ∙OH) [60]










2[89]






cyanide (K3Fe(CN)


11H13N3O)




(a) (b)

(c)







2CO3NaHCO

3



350 400 450 500 550 600 650 7000

1000000

2000000

3000000

4000000

5000000In

tens

ity (C

PS)


(a3) (a4)

(a)

(b1)

(b3)

(b2)

(b)



2) rectifier





2-Ta2O5 TiSnO



2-Ta2O5and TiSnO






2SO4K2SO4(SAT) 119864∘ = 0640V





2-Ta2O5and TiSnO









2SO4







removal = [(119862119900minus 119862119891)

119862119900

] lowast 100 (3)


3 Results





5COD = 009 and 007



4










10284250 72450 [1] 320100 [3] 3150 [97] 100 [16] 4450 [18] 2323 [13] 257 [17]590 [9] 602 [7] 935 [19] 2746 [98] 1220 [96]


pH 1302 1350 1297 [1] 13 [3] 8 [16] 860 [18] 805 [13] 760 [17] 920 [7] 810[19] 759 [98] 10 [96]








2O2 to






2-Ta2O5and







OH

CH3

CH3

(a)

OH

(b)

CH3

OH

(c)

OH

H3C

(d)

OH

CH3

(e)



Ta (a2) Sn (b

1) B (c

1) and C (c




2Sb2O3and Sb



2-Ta2O5and TiSnO



2-Ta2O5(d1) TiSnO

2-Sb (d

2) and TiBDD

(d3) in 05M H






2







minus01

00

01

02

03

04

(d)

(c)

(b)

(a)

j(m

Acm

minus2 )

(a1) (a2)

(c1) (c2)

(b1)

(d1)

(d2)

(d3)

E(V) vs HgHg2SO4




2) Ta (b

1) Sn (c

1) B and (c


1) TiIrO

2-Ta2O5 (d2) TiSnO

2-


2SO4


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)






4[63 104] and HNO





2SO4


2SO4(Figure 5(a))



0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



2 TiRuO



2-Sb


2andwater due to


2)






2-



3 H2O2 and ∙OH) [60]










2[89]






cyanide (K3Fe(CN)


11H13N3O)




(a) (b)

(c)







2CO3NaHCO

3



350 400 450 500 550 600 650 7000

1000000

2000000

3000000

4000000

5000000In

tens

ity (C

PS)


(a3) (a4)

(a)

(b1)

(b3)

(b2)

(b)



2) rectifier





2-Ta2O5 TiSnO



2-Ta2O5and TiSnO






2SO4K2SO4(SAT) 119864∘ = 0640V





2-Ta2O5and TiSnO









2SO4







removal = [(119862119900minus 119862119891)

119862119900

] lowast 100 (3)


3 Results





5COD = 009 and 007



4










10284250 72450 [1] 320100 [3] 3150 [97] 100 [16] 4450 [18] 2323 [13] 257 [17]590 [9] 602 [7] 935 [19] 2746 [98] 1220 [96]


pH 1302 1350 1297 [1] 13 [3] 8 [16] 860 [18] 805 [13] 760 [17] 920 [7] 810[19] 759 [98] 10 [96]








2O2 to






2-Ta2O5and







OH

CH3

CH3

(a)

OH

(b)

CH3

OH

(c)

OH

H3C

(d)

OH

CH3

(e)



Ta (a2) Sn (b

1) B (c

1) and C (c




2Sb2O3and Sb



2-Ta2O5and TiSnO



2-Ta2O5(d1) TiSnO

2-Sb (d

2) and TiBDD

(d3) in 05M H






2







minus01

00

01

02

03

04

(d)

(c)

(b)

(a)

j(m

Acm

minus2 )

(a1) (a2)

(c1) (c2)

(b1)

(d1)

(d2)

(d3)

E(V) vs HgHg2SO4




2) Ta (b

1) Sn (c

1) B and (c


1) TiIrO

2-Ta2O5 (d2) TiSnO

2-


2SO4


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)






4[63 104] and HNO





2SO4


2SO4(Figure 5(a))



0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(a) (b)

(c)







2CO3NaHCO

3



350 400 450 500 550 600 650 7000

1000000

2000000

3000000

4000000

5000000In

tens

ity (C

PS)


(a3) (a4)

(a)

(b1)

(b3)

(b2)

(b)



2) rectifier





2-Ta2O5 TiSnO



2-Ta2O5and TiSnO






2SO4K2SO4(SAT) 119864∘ = 0640V





2-Ta2O5and TiSnO









2SO4







removal = [(119862119900minus 119862119891)

119862119900

] lowast 100 (3)


3 Results





5COD = 009 and 007



4










10284250 72450 [1] 320100 [3] 3150 [97] 100 [16] 4450 [18] 2323 [13] 257 [17]590 [9] 602 [7] 935 [19] 2746 [98] 1220 [96]


pH 1302 1350 1297 [1] 13 [3] 8 [16] 860 [18] 805 [13] 760 [17] 920 [7] 810[19] 759 [98] 10 [96]








2O2 to






2-Ta2O5and







OH

CH3

CH3

(a)

OH

(b)

CH3

OH

(c)

OH

H3C

(d)

OH

CH3

(e)



Ta (a2) Sn (b

1) B (c

1) and C (c




2Sb2O3and Sb



2-Ta2O5and TiSnO



2-Ta2O5(d1) TiSnO

2-Sb (d

2) and TiBDD

(d3) in 05M H






2







minus01

00

01

02

03

04

(d)

(c)

(b)

(a)

j(m

Acm

minus2 )

(a1) (a2)

(c1) (c2)

(b1)

(d1)

(d2)

(d3)

E(V) vs HgHg2SO4




2) Ta (b

1) Sn (c

1) B and (c


1) TiIrO

2-Ta2O5 (d2) TiSnO

2-


2SO4


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)






4[63 104] and HNO





2SO4


2SO4(Figure 5(a))



0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


350 400 450 500 550 600 650 7000

1000000

2000000

3000000

4000000

5000000In

tens

ity (C

PS)


(a3) (a4)

(a)

(b1)

(b3)

(b2)

(b)



2) rectifier





2-Ta2O5 TiSnO



2-Ta2O5and TiSnO






2SO4K2SO4(SAT) 119864∘ = 0640V





2-Ta2O5and TiSnO









2SO4







removal = [(119862119900minus 119862119891)

119862119900

] lowast 100 (3)


3 Results





5COD = 009 and 007



4










10284250 72450 [1] 320100 [3] 3150 [97] 100 [16] 4450 [18] 2323 [13] 257 [17]590 [9] 602 [7] 935 [19] 2746 [98] 1220 [96]


pH 1302 1350 1297 [1] 13 [3] 8 [16] 860 [18] 805 [13] 760 [17] 920 [7] 810[19] 759 [98] 10 [96]








2O2 to






2-Ta2O5and







OH

CH3

CH3

(a)

OH

(b)

CH3

OH

(c)

OH

H3C

(d)

OH

CH3

(e)



Ta (a2) Sn (b

1) B (c

1) and C (c




2Sb2O3and Sb



2-Ta2O5and TiSnO



2-Ta2O5(d1) TiSnO

2-Sb (d

2) and TiBDD

(d3) in 05M H






2







minus01

00

01

02

03

04

(d)

(c)

(b)

(a)

j(m

Acm

minus2 )

(a1) (a2)

(c1) (c2)

(b1)

(d1)

(d2)

(d3)

E(V) vs HgHg2SO4




2) Ta (b

1) Sn (c

1) B and (c


1) TiIrO

2-Ta2O5 (d2) TiSnO

2-


2SO4


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)






4[63 104] and HNO





2SO4


2SO4(Figure 5(a))



0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





2SO4







removal = [(119862119900minus 119862119891)

119862119900

] lowast 100 (3)


3 Results





5COD = 009 and 007



4










10284250 72450 [1] 320100 [3] 3150 [97] 100 [16] 4450 [18] 2323 [13] 257 [17]590 [9] 602 [7] 935 [19] 2746 [98] 1220 [96]


pH 1302 1350 1297 [1] 13 [3] 8 [16] 860 [18] 805 [13] 760 [17] 920 [7] 810[19] 759 [98] 10 [96]








2O2 to






2-Ta2O5and







OH

CH3

CH3

(a)

OH

(b)

CH3

OH

(c)

OH

H3C

(d)

OH

CH3

(e)



Ta (a2) Sn (b

1) B (c

1) and C (c




2Sb2O3and Sb



2-Ta2O5and TiSnO



2-Ta2O5(d1) TiSnO

2-Sb (d

2) and TiBDD

(d3) in 05M H






2







minus01

00

01

02

03

04

(d)

(c)

(b)

(a)

j(m

Acm

minus2 )

(a1) (a2)

(c1) (c2)

(b1)

(d1)

(d2)

(d3)

E(V) vs HgHg2SO4




2) Ta (b

1) Sn (c

1) B and (c


1) TiIrO

2-Ta2O5 (d2) TiSnO

2-


2SO4


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)






4[63 104] and HNO





2SO4


2SO4(Figure 5(a))



0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







10284250 72450 [1] 320100 [3] 3150 [97] 100 [16] 4450 [18] 2323 [13] 257 [17]590 [9] 602 [7] 935 [19] 2746 [98] 1220 [96]


pH 1302 1350 1297 [1] 13 [3] 8 [16] 860 [18] 805 [13] 760 [17] 920 [7] 810[19] 759 [98] 10 [96]








2O2 to






2-Ta2O5and







OH

CH3

CH3

(a)

OH

(b)

CH3

OH

(c)

OH

H3C

(d)

OH

CH3

(e)



Ta (a2) Sn (b

1) B (c

1) and C (c




2Sb2O3and Sb



2-Ta2O5and TiSnO



2-Ta2O5(d1) TiSnO

2-Sb (d

2) and TiBDD

(d3) in 05M H






2







minus01

00

01

02

03

04

(d)

(c)

(b)

(a)

j(m

Acm

minus2 )

(a1) (a2)

(c1) (c2)

(b1)

(d1)

(d2)

(d3)

E(V) vs HgHg2SO4




2) Ta (b

1) Sn (c

1) B and (c


1) TiIrO

2-Ta2O5 (d2) TiSnO

2-


2SO4


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)






4[63 104] and HNO





2SO4


2SO4(Figure 5(a))



0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





OH

CH3

CH3

(a)

OH

(b)

CH3

OH

(c)

OH

H3C

(d)

OH

CH3

(e)



Ta (a2) Sn (b

1) B (c

1) and C (c




2Sb2O3and Sb



2-Ta2O5and TiSnO



2-Ta2O5(d1) TiSnO

2-Sb (d

2) and TiBDD

(d3) in 05M H






2







minus01

00

01

02

03

04

(d)

(c)

(b)

(a)

j(m

Acm

minus2 )

(a1) (a2)

(c1) (c2)

(b1)

(d1)

(d2)

(d3)

E(V) vs HgHg2SO4




2) Ta (b

1) Sn (c

1) B and (c


1) TiIrO

2-Ta2O5 (d2) TiSnO

2-


2SO4


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)






4[63 104] and HNO





2SO4


2SO4(Figure 5(a))



0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



minus01

00

01

02

03

04

(d)

(c)

(b)

(a)

j(m

Acm

minus2 )

(a1) (a2)

(c1) (c2)

(b1)

(d1)

(d2)

(d3)

E(V) vs HgHg2SO4




2) Ta (b

1) Sn (c

1) B and (c


1) TiIrO

2-Ta2O5 (d2) TiSnO

2-


2SO4


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)






4[63 104] and HNO





2SO4


2SO4(Figure 5(a))



0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


240 260 280 300 32000

02

04

06

08

10Ab

sorb

ance

(au

)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(a)

240 260 280 300 32000

02

04

06

08

10

Abso

rban

ce (a

u)


pH 7 pH 8 pH 9 pH 10 pH 11 pH 12

120582 (nm)

(b)

0

100

200

300

Redo

x po

tent

ial

minus300

minus200

minus100pH 1ndash12

(c)






4[63 104] and HNO





2SO4


2SO4(Figure 5(a))



0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 1 2 3

000

004

008

012


minus004

j(m

Acm

minus2 )

(a1)

(a2)

E(V) vs HgHg2SO4

(a)

0 2 4 6 8 1005

06

07

08

09

10

Nor

mal

ized

inte

nsity

(au

)

t (min)

(b1)

(b2)

(b)

00 01 02 03 0400

02

04

06

08

10

Phen

ol (C

Co)

j (A cmminus2)

(c)


2) 005M



2) 005M NaOHH

2SO4




2SO4










0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 2 4 6 8 10 1200

02

04

06

08

10



(a) (b) (c)

t (h)

CC

o


2SO4) and 119905






2SO4(pH 1) with the


2SO4) In this anal-


HOCl + ℎ] 997888rarr ∙OH + ∙Cl (4)














8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


8h 12h0h

(a)

0h 8h 12h

(b)

0h 8h 12h

(c)


2SO4)

and 119905119903= 12 h



COD removal()


TOC(mg Lminus1)

TOC removal()








119903= 15 h) is shown



(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(a) (b)

(c) (d)


2SO4) and 119905

119903= 15 h


4 Conclusions






Acknowledgments


References












































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of









































2anoderdquo

























2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






















2-Pt and




































2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




















2anodesrdquo
















2-Ta2O5and BDD in































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

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